Structure of a membrane keypad
A membrane keyboard consists of several layers that are firmly glued together. The bonded layers cannot be separated without damage, so it is usually not possible to repair a membrane keypad. The keyboard itself is also firmly glued to the device, which makes it difficult to remove the membrane keyboard without damaging it. The picture shows a schematic side view of a membrane keyboard. Below you will find a brief explanation of the layers.
Top layer of the keyboard
The top layer of the membrane keypad consists of a printed, abrasion-resistant plastic film with an adhesive surface on the back. The adhesive is cut out on the key surfaces so that the foil does not stick to the actual key. Optionally, the foil can be embossed on the keys, which makes the key visually stand out from the rest of the foil and is tactile.
This layer is optional and is usually a clear plastic film. This is used to provide more space for the snap-on discs (also known as the Knackfrosch ) or to provide the rubber buttons. If the buttons are embossed in the front foil, this layer is usually not necessary.
The second layer is the actual electronics of the keyboard and consists of a printed circuit board or conductor foil. Depending on the design of the membrane keypad, the layer consists of a conductor foil with click frogs or a conductive rubber button, or of two glued conductor foils that are pressed together by the keystroke. This layer is then glued to the device via adhesive. The electronic layer is connected to the actual device either with a plug or with an extended foil board (flex board).